To be as economical as possible, applications for distributing digital works in niche markets should use media, playback equipment and display systems that are similar to mass-market versions produced for consumer or business applications. Typically, such digital works are subdivided into a multiplicity of data objects.
Co-pending U.S. patent application Ser. No. 09/519,253, filed on Mar. 6, 2000 in the name of Terence J. Nelson entitled “METHOD FOR RENDERING UNAUTHORIZED COPIES OF DIGITAL CONTENT TRACEABLE TO AUTHORIZED COPIES” which is incorporated herein by reference describes a method for creating digital works that may be traced to a particular individual. By this method, bits of license-enforcement data are embedded in a licensed copy of a digital work implicitly, by choosing one of a plurality of digitally distinct versions of each of a selected plurality of the data objects. These versions are advantageously prepared during the creation of a digital work so that each has the effect that the artist intended. The content, being customized, is delivered to a customer by means of a suitable writable media or by other methods that can be made secure.
Another key step in the method of the co-pending application is to inform customers, in advance, that their copy of the digital work will be customized for them. This knowledge will substantially inhibit customers from making and giving away second-generation copies because the small benefit is not worth the risk of encountering the copyright holder's enforcement processes.
DVD-Video can also be used advantageously in niche markets where so-called “early window” material is screened. However, extra precautions are needed to ensure that high-quality analog copies are not illicitly made and distributed. In particular, it is useful to prepare modified players to play modified discs that do not produce acceptable output in unmodified DVD-Video players. This may be done, for example, by encoding the video data onto the DVD using an encryption code or an encryption method that is not supported by consumer-market players. This complicates the task of obtaining an analog copy because access to the modified players would normally be restricted.
Operators of the early-window application, however, may be able to make analog copies without being detected. Therefore, it is also useful to be able to hold those persons with access to the DVD and the players, for example, flight attendants and mechanics, accountable for the discs and modified players entrusted to them. Accordingly, there is a need to provide a method of tracing analog copies of digital content delivered on writable media to the particular media and player responsible.
Providing the ability to trace an analog copy to a player raises the issue of extra cost in implementing an encoding function in a player. Thus, it is advantageous if the inventive system relies on an existing feature of DVD-Video to support this capability.